Field of the Invention
The present invention relates to a high frequency filter including a plurality of insulator layers and transmission lines.
Description of the Related Art
As one of conventional high frequency filters, for example, a multilayer balanced filter described in Japanese Unexamined Patent Application Publication No. 2011-124880 is known. The multilayer balanced filter described in Japanese Unexamined Patent Application Publication No. 2011-124880 is described below. FIG. 10 is an exploded perspective view of a multilayer structure of the multilayer balanced filter 500 described in Japanese Unexamined Patent Application Publication No. 2011-124880. FIG. 11 is an equivalent circuit diagram of the multilayer balanced filter 500 described in Japanese Unexamined Patent Application Publication No. 2011-124880.
As illustrated in FIG. 10, the multilayer balanced filter 500 includes the multilayer structure 502, coils 531, 541 to 543, capacitor electrodes 521 to 523, and a ground electrode 520. The multilayer structure 502 is formed by stacking a plurality of dielectric layers 550 to 556.
The coils 531 and 541 are formed on the dielectric layer 553. The coil 542 is formed on the dielectric layer 552. The coil 543 is formed on the dielectric layer 551. The coil 531 electromagnetically couples to the coil 542 with the dielectric layer 552 in between by arranging the coil 531 and the coil 542 to oppose each other in a stacking direction of the multilayer structure 502. Further, one end portion of the coil 542 is connected to the coil 541 through a via-hole conductor. The other end portion of the coil 542 is connected to the coil 543 through a via-hole conductor.
The capacitor electrode 521 is formed on the dielectric layer 554. The capacitor electrodes 522 and 523 are formed on the dielectric layer 556. Further, the ground electrode 520 is formed on the dielectric layer 555.
A capacitor C100 is formed by arranging the ground electrode 520 and the capacitor electrode 521 so as to oppose each other across the dielectric layer 554. Further, the capacitor C100 is connected in parallel to the coil 531. As illustrated in FIG. 11, the capacitor C100 and the coil 531 form part of the multilayer balanced filter 500.
Further, a capacitor C200 is formed by arranging the ground electrode 520 and the capacitor electrode 522 so as to oppose each other across the dielectric layer 555. Further, the capacitor C200 is connected to the coil 541. As illustrated in FIG. 11, the capacitor C200 and the coil 541 form part of the multilayer balanced filter 500.
Further, a capacitor C300 is formed by arranging the ground electrode 520 and the capacitor electrode 523 so as to oppose each other across the dielectric layer 555. Further, the capacitor C300 is connected to the coil 543. As illustrated in FIG. 11, the capacitor C300 and the coil 543 form part of the multilayer balanced filter 500.
In the multilayer balanced filter 500 configured as described above, an unbalanced signal inputted from an input terminal 561 to the coil 531 is converted to a balanced signal in between the coil 531 and the coil 542, as illustrated in FIG. 11. The balanced signal is transmitted from the coil 542 to the coil 541 and the coil 543, and outputted from output terminals 562 and 563.
In the multilayer balanced filter 500, the coil 531 and the coil 542 are electromagnetically coupled by arranging them to oppose each other in the stacking direction with the dielectric layer 552 in between (broadside coupling). Accordingly, in the multilayer balanced filter 500, the area of insulator layers may be reduced compared to a multilayer balanced filter in which two coils are arranged on the same layer to produce electromagnetic coupling (edge coupling).
However, in the multilayer balanced filter 500, the coil 531 and the coil 542 face each other in the stacking direction. Thus, compared to the multilayer balanced filter in which two coils are arranged on the same layer to produce electromagnetic coupling, the multilayer balanced filter 500 stacks more insulator layers. In other words, it is difficult to reduce a profile height of the multilayer balanced filter 500.